Many of the industrially important ethylenically unsaturated monomers are highly susceptible to unwanted radical polymerization initiated either thermally or by adventitious impurities. Some examples of these monomers are styrene, acrylic and methacrylic acid, acrylate and methacrylate esters and acrylonitrile. Premature polymerization may occur during manufacture, purification or storage of the monomer. Many of these monomers are purified by distillation. It is in this operation where premature polymerization is most likely to occur and to be the most troublesome. Methods to prevent or reduce the amount of such polymerization are thus highly desirable since the prevention or mitigation of such premature polymerization increases the yield of purified monomer and also insures against costly and potentially dangerous runaway polymerization in the plant.
Stable hindered organic nitroxyl compounds included in this invention are those nitroxides which are fully substituted at the alpha carbon atoms. See L. B. Volodarsky et al., Synthetic Chemistry of Stable Nitroxides, CRC Press, Boca Raton, Fla., 1994. Bis-tri-fluoromethylnitroxide is a stable nitroxide and its 1,2-bis-adducts with ethylenes are known. See A. E. Tipping et al., J. Fluor. Chem., 69, 163 (1994); R. E. Banks et al., J. Chem. Soc. C, 901 (1966); and R. E. Banks et al., J. Chem. Soc., C, 2777 (1971).
1-Phenyl-1,2-bis(2,2,6,6-tetramethylpiperidin-1-yloxy)-ethane and 1-phenyl-1,2-bis(1,1,3,3-tetramethylisoindolin-2-yloxy)ethane are known bis-adducts as taught by G. Moad et al., Polymer Bull. 6, 589 (1982) who reported these materials as prepared by the reaction of 1-oxyl-2,2,6,6-tetramethylpiperidine and 2-oxyl-1,1,3,3-tetramethylisoindoline with styrene. No chemical Abstract Number was ever assigned to this first compound nor was any utility ever ascribed to such compounds.
T. J. Connolly et al., Tetrahedron Letters, 38, 1133 (1997) in a recently issued paper issued note that TEMPO (1-oxyl-2,2,6,6-tetramethylpiperidine) reacts with styrene and polystyrene to mediate autopolymerization and effect the polydispersity of polystyrene in "living" polymer systems.